1. Field of the Invention
The present invention relates generally to HROM replication methods, devices or systems. The present invention also relates to articles comprising a conical reference (reconstruction) beam hologram element to generate conical or conical like reference (reconstruction) beams which may be used in such HROM replication methods, systems or devices. The present invention further relates to an article comprising a target holographic storage medium which may be used in such HROM replication methods, devices or systems.
2. Related Art
Developers of information storage devices and methods continue to seek increased storage capacity. As part of this development, holographic memory systems have been suggested as alternatives to conventional memory devices. Holographic memory systems may be designed to record data as one bit of information (i.e., bit-wise data storage). See McLeod et al. “Micro-Holographic Multi-Layer Optical Disk Data Storage,” International Symposium on Optical Memory and Optical Data Storage (July 2005). Holographic memory systems may also be designed to record an array of data that may be a 1-dimensional linear array (i.e., a 1×N array, where N is the number linear data bits), or a 2-dimensional array commonly referred to as a “page-wise” memory system. Page-wise memory systems may involve the storage and readout of an entire two-dimensional representation, e.g., a page of data. Typically, recording light passes through a two-dimensional array of low and high transparency areas representing data, and the system stores, in three dimensions, the pages of data holographically as patterns of varying refractive index imprinted into a storage medium. See Psaltis et al., “Holographic Memories,” Scientific American, November 1995, where holographic systems are discussed generally, including page-wise memory systems.
Holographic data storage systems may perform a data write (also referred to as a data record or data store operation, simply “write” operation herein) by combining two coherent light beams, such as laser beams, at a particular point within the storage medium. Specifically, a data-encoded light beam may be combined with a reference light beam to create an interference pattern in the holographic storage medium. The pattern created by the interference of the data beam and the reference beam forms a hologram which may then be recorded in the holographic medium. If the data-bearing beam is encoded by passing the data beam through, for example, a spatial light modulator (SLM), the hologram(s) may be recorded in the holographic medium.
Holographically-stored data may then be retrieved from the holographic data storage system by performing a read (or reconstruction) of the stored data. The read operation may be performed by projecting a reconstruction or probe beam into the storage medium at the same angle, wavelength, phase, position, etc., as the reference beam used to record the data, or compensated equivalents thereof. The hologram and the reference beam interact to reconstruct the data beam.
Holographic Read Only Memory (Holographic ROM or HROM) storage media are known. In the past, holographic data has been recorded in disc format HROM in an incremental manner by successively aligning different locations on the HROM with the data beam and the reference beam to record successive data bits. Different data may be recorded at each successive location by changing the information imparted through a spatial light modulator (SLM) or successive data masks. See, for example, U.S. Pat. No. 6,272,095, (Liu, et al.), issued Aug. 7, 2001, which describes several examples of illustrative prior recording techniques, and is incorporated herein by reference in its entirety. Multiple holograms may also be stacked in virtual image layers through wavelength multiplexing, angle multiplexing, shift multiplexing, confocal multiplexing, or other multiplexing techniques. Each hologram in a stack may comprise a page of information, where a “page” is a collection of bits or of pixel data stored together, e.g., as a 2048×2048 array or a 10×10 array. See U.S. Pat. No. 6,322,933, (Daiber et al.), issued Nov. 27, 2001, which describes several examples of illustrative prior volume recording techniques. See also Ernest Chuang, et al. “Holographic ROM System for High Speed Replication,” presented at the Optical Data Storage Conference, Jul. 8, 2002, in Hawaii, USA., and Ernest Chuang, et al. “Holographic Read-Only-Memory System for High-Speed Replication,” Jpn. J. Appl. Phys., 42 (2003), pp. 976-80, which also describe recording techniques and the bitwise retrieval of an HROM.